add zero-diagonal constraint checks for is_skew_symmetric

[srinjoy933]

solve #1168

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 68.04%. Comparing base (dae9d4b) to head (bd8022e).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1169   +/-   ##
=======================================
  Coverage   68.04%   68.04%           
=======================================
  Files         404      404           
  Lines       12948    12948           
  Branches     1395     1395           
=======================================
  Hits         8810     8810           
  Misses       4138     4138           

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[srinjoy933]

hey @jalvesz @jvdp1 please have a look on this pr and please suggest me if any changes are required

[Copilot]

Pull request overview

This PR strengthens the is_skew_symmetric test coverage in the linalg test suite by adding explicit validation of the zero-diagonal requirement for skew-symmetric matrices (per issue #1168).

Changes:

• Adds a new A_false_diag test matrix (per type/kind) that is off-diagonally skew-symmetric but has a non-zero diagonal entry.
• Extends the test_is_skew_symmetric_* checks to assert is_skew_symmetric(A_false_diag) returns .false. for real, complex (including purely imaginary diagonal), and integer cases.

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[jvdp1]

thank you @srinjoy933
As it is only adding tests, I will approve and merge this PR.